I can't myself see the connection between a hefty blow to the head and a whisper.
The word 'wisty' has been used in Lancashire for 'large', but in relation to space. eg 'She had a wisty parlour'.

In Cockney rhyming slang, castor refers to Castor and Pollox (in other words, bollocks - testicles) If one is kicked in the castors, one is not a happy bunny.

Clyster is pronounced so as to rhyme with sheister. Clyster and clister both refer to an enema.